One, it's too frequent an occurrence to be noteworthy. Two, it could result in eye contact with a crazy person which is something to be avoided at all costs.

Instead we all look in the opposite direction of the insane person just a few feet away from us, while also watching their reflections in the window glass to make sure we don't get blindsided if they turn stabby.

Dunno how it is in Thailand, but in some Asian countries a lot of people try and catch some shut eye whilst on the train. It's pretty inappropriate to disturb people from their thoughts just for a throwaway photo.